As the advances of the networking technologies, the compression techniques and the storage devices, computer media are widely utilized in many applications, such as entertainment and education. When the video media is the case, the video contents are usually stored as a sequence of frames where each frame represents a single image snapshot. During the play-back, the timing of play-back of the video is critical in maintaining the quality of the video. Especially in the case of remote play-back, each frame has to be delivered to and played-back by the user work station within a time limit in order not to produce observable jitters.
Another reason for the timing constraint is to synchronize the video media with other media, such as voice and text, in a multimedia application. In order to sustain the system with high quality-of-service (QoS), the storage system has to guarantee its performance as it plays a major role in supporting a real-time video media.
Besides the real-time criteria, designing a video storage system needs to deal with the storing and the retrieving of large amount of video data. Compression techniques are popular in reducing the size of the video files. For instance, the MPEG 1 data compression standard can reduce the file size up to one fortieth of the original. Due to the nature of the compression algorithms, the compressed video frames have variable sizes where the term VBR video comes from.
In order to improve the throughput of the disks, the conventional design of the storage systems are focused on the scheduling and the data placement of the disks so that the seeking time of the data may be reduced. Of late, zoning technique has been developed to increase the capacities disks. Under the zoning design, a zone in a disk comprises a group of contiguous track with the equivalent number of sectors per track. There are typically 3 to 20 zones on a hard disk, and the number is likely to be doubled by the end of this decade. FIG. 1 shows the distribution of zones and tracks of a zoned disk with 3 zones. In order to fully use the disks' magnetized surface, there are more sectors in the outer zones than in the inner zones. In other words, the outer zones have larger track size then has the inner zones. Another effect of disk zoning is that the disk has higher data transfer rates (or bandwidths) in the outer zones than in the inner zones, as disks spin at a constant angular velocity. Such zoning technology helps to increase the throughput of disks of video servers. Generally speaking, storing larger and more frequently accessed blocks in the outer zones, and smaller and less frequently accessed blocks in the inner zones can obtain higher average throughput.